1 files changed, 529 insertions, 164 deletions

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index bd38c5cfd8ad..960cbf44c844 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -4,21 +4,92 @@
  * Copyright (C) 2008 Steven Rostedt <srostedt@redhat.com>
  */
 #include <linux/ring_buffer.h>
+#include <linux/trace_clock.h>
+#include <linux/ftrace_irq.h>
 #include <linux/spinlock.h>
 #include <linux/debugfs.h>
 #include <linux/uaccess.h>
+#include <linux/hardirq.h>
 #include <linux/module.h>
 #include <linux/percpu.h>
 #include <linux/mutex.h>
-#include <linux/sched.h>	/* used for sched_clock() (for now) */
 #include <linux/init.h>
 #include <linux/hash.h>
 #include <linux/list.h>
+#include <linux/cpu.h>
 #include <linux/fs.h>
 
 #include "trace.h"
 
 /*
+ * The ring buffer is made up of a list of pages. A separate list of pages is
+ * allocated for each CPU. A writer may only write to a buffer that is
+ * associated with the CPU it is currently executing on.  A reader may read
+ * from any per cpu buffer.
+ *
+ * The reader is special. For each per cpu buffer, the reader has its own
+ * reader page. When a reader has read the entire reader page, this reader
+ * page is swapped with another page in the ring buffer.
+ *
+ * Now, as long as the writer is off the reader page, the reader can do what
+ * ever it wants with that page. The writer will never write to that page
+ * again (as long as it is out of the ring buffer).
+ *
+ * Here's some silly ASCII art.
+ *
+ *   +------+
+ *   |reader|          RING BUFFER
+ *   |page  |
+ *   +------+        +---+   +---+   +---+
+ *                   |   |-->|   |-->|   |
+ *                   +---+   +---+   +---+
+ *                     ^               |
+ *                     |               |
+ *                     +---------------+
+ *
+ *
+ *   +------+
+ *   |reader|          RING BUFFER
+ *   |page  |------------------v
+ *   +------+        +---+   +---+   +---+
+ *                   |   |-->|   |-->|   |
+ *                   +---+   +---+   +---+
+ *                     ^               |
+ *                     |               |
+ *                     +---------------+
+ *
+ *
+ *   +------+
+ *   |reader|          RING BUFFER
+ *   |page  |------------------v
+ *   +------+        +---+   +---+   +---+
+ *      ^            |   |-->|   |-->|   |
+ *      |            +---+   +---+   +---+
+ *      |                              |
+ *      |                              |
+ *      +------------------------------+
+ *
+ *
+ *   +------+
+ *   |buffer|          RING BUFFER
+ *   |page  |------------------v
+ *   +------+        +---+   +---+   +---+
+ *      ^            |   |   |   |-->|   |
+ *      |   New      +---+   +---+   +---+
+ *      |  Reader------^               |
+ *      |   page                       |
+ *      +------------------------------+
+ *
+ *
+ * After we make this swap, the reader can hand this page off to the splice
+ * code and be done with it. It can even allocate a new page if it needs to
+ * and swap that into the ring buffer.
+ *
+ * We will be using cmpxchg soon to make all this lockless.
+ *
+ */
+
+/*
  * A fast way to enable or disable all ring buffers is to
  * call tracing_on or tracing_off. Turning off the ring buffers
  * prevents all ring buffers from being recorded to.
@@ -57,7 +128,9 @@ enum {
 	RB_BUFFERS_DISABLED	= 1 << RB_BUFFERS_DISABLED_BIT,
 };
 
-static long ring_buffer_flags __read_mostly = RB_BUFFERS_ON;
+static unsigned long ring_buffer_flags __read_mostly = RB_BUFFERS_ON;
+
+#define BUF_PAGE_HDR_SIZE offsetof(struct buffer_data_page, data)
 
 /**
  * tracing_on - enable all tracing buffers
@@ -89,59 +162,92 @@ EXPORT_SYMBOL_GPL(tracing_off);
  * tracing_off_permanent - permanently disable ring buffers
  *
  * This function, once called, will disable all ring buffers
- * permanenty.
+ * permanently.
  */
 void tracing_off_permanent(void)
 {
 	set_bit(RB_BUFFERS_DISABLED_BIT, &ring_buffer_flags);
 }
 
+/**
+ * tracing_is_on - show state of ring buffers enabled
+ */
+int tracing_is_on(void)
+{
+	return ring_buffer_flags == RB_BUFFERS_ON;
+}
+EXPORT_SYMBOL_GPL(tracing_is_on);
+
 #include "trace.h"
 
-/* Up this if you want to test the TIME_EXTENTS and normalization */
-#define DEBUG_SHIFT 0
+#define RB_EVNT_HDR_SIZE (offsetof(struct ring_buffer_event, array))
+#define RB_ALIGNMENT		4U
+#define RB_MAX_SMALL_DATA	28
+
+enum {
+	RB_LEN_TIME_EXTEND = 8,
+	RB_LEN_TIME_STAMP = 16,
+};
 
-/* FIXME!!! */
-u64 ring_buffer_time_stamp(int cpu)
+static inline int rb_null_event(struct ring_buffer_event *event)
 {
-	u64 time;
+	return event->type == RINGBUF_TYPE_PADDING && event->time_delta == 0;
+}
 
-	preempt_disable_notrace();
-	/* shift to debug/test normalization and TIME_EXTENTS */
-	time = sched_clock() << DEBUG_SHIFT;
-	preempt_enable_no_resched_notrace();
+static inline int rb_discarded_event(struct ring_buffer_event *event)
+{
+	return event->type == RINGBUF_TYPE_PADDING && event->time_delta;
+}
 
-	return time;
+static void rb_event_set_padding(struct ring_buffer_event *event)
+{
+	event->type = RINGBUF_TYPE_PADDING;
+	event->time_delta = 0;
 }
-EXPORT_SYMBOL_GPL(ring_buffer_time_stamp);
 
-void ring_buffer_normalize_time_stamp(int cpu, u64 *ts)
+/**
+ * ring_buffer_event_discard - discard an event in the ring buffer
+ * @buffer: the ring buffer
+ * @event: the event to discard
+ *
+ * Sometimes a event that is in the ring buffer needs to be ignored.
+ * This function lets the user discard an event in the ring buffer
+ * and then that event will not be read later.
+ *
+ * Note, it is up to the user to be careful with this, and protect
+ * against races. If the user discards an event that has been consumed
+ * it is possible that it could corrupt the ring buffer.
+ */
+void ring_buffer_event_discard(struct ring_buffer_event *event)
 {
-	/* Just stupid testing the normalize function and deltas */
-	*ts >>= DEBUG_SHIFT;
+	event->type = RINGBUF_TYPE_PADDING;
+	/* time delta must be non zero */
+	if (!event->time_delta)
+		event->time_delta = 1;
 }
-EXPORT_SYMBOL_GPL(ring_buffer_normalize_time_stamp);
 
-#define RB_EVNT_HDR_SIZE (sizeof(struct ring_buffer_event))
-#define RB_ALIGNMENT_SHIFT	2
-#define RB_ALIGNMENT		(1 << RB_ALIGNMENT_SHIFT)
-#define RB_MAX_SMALL_DATA	28
+static unsigned
+rb_event_data_length(struct ring_buffer_event *event)
+{
+	unsigned length;
 
-enum {
-	RB_LEN_TIME_EXTEND = 8,
-	RB_LEN_TIME_STAMP = 16,
-};
+	if (event->len)
+		length = event->len * RB_ALIGNMENT;
+	else
+		length = event->array[0];
+	return length + RB_EVNT_HDR_SIZE;
+}
 
 /* inline for ring buffer fast paths */
-static inline unsigned
+static unsigned
 rb_event_length(struct ring_buffer_event *event)
 {
-	unsigned length;
-
 	switch (event->type) {
 	case RINGBUF_TYPE_PADDING:
-		/* undefined */
-		return -1;
+		if (rb_null_event(event))
+			/* undefined */
+			return -1;
+		return rb_event_data_length(event);
 
 	case RINGBUF_TYPE_TIME_EXTEND:
 		return RB_LEN_TIME_EXTEND;
@@ -150,11 +256,7 @@ rb_event_length(struct ring_buffer_event *event)
 		return RB_LEN_TIME_STAMP;
 
 	case RINGBUF_TYPE_DATA:
-		if (event->len)
-			length = event->len << RB_ALIGNMENT_SHIFT;
-		else
-			length = event->array[0];
-		return length + RB_EVNT_HDR_SIZE;
+		return rb_event_data_length(event);
 	default:
 		BUG();
 	}
@@ -179,7 +281,7 @@ unsigned ring_buffer_event_length(struct ring_buffer_event *event)
 EXPORT_SYMBOL_GPL(ring_buffer_event_length);
 
 /* inline for ring buffer fast paths */
-static inline void *
+static void *
 rb_event_data(struct ring_buffer_event *event)
 {
 	BUG_ON(event->type != RINGBUF_TYPE_DATA);
@@ -209,7 +311,7 @@ EXPORT_SYMBOL_GPL(ring_buffer_event_data);
 
 struct buffer_data_page {
 	u64		 time_stamp;	/* page time stamp */
-	local_t		 commit;	/* write commited index */
+	local_t		 commit;	/* write committed index */
 	unsigned char	 data[];	/* data of buffer page */
 };
 
@@ -225,14 +327,25 @@ static void rb_init_page(struct buffer_data_page *bpage)
 	local_set(&bpage->commit, 0);
 }
 
+/**
+ * ring_buffer_page_len - the size of data on the page.
+ * @page: The page to read
+ *
+ * Returns the amount of data on the page, including buffer page header.
+ */
+size_t ring_buffer_page_len(void *page)
+{
+	return local_read(&((struct buffer_data_page *)page)->commit)
+		+ BUF_PAGE_HDR_SIZE;
+}
+
 /*
  * Also stolen from mm/slob.c. Thanks to Mathieu Desnoyers for pointing
  * this issue out.
  */
-static inline void free_buffer_page(struct buffer_page *bpage)
+static void free_buffer_page(struct buffer_page *bpage)
 {
-	if (bpage->page)
-		free_page((unsigned long)bpage->page);
+	free_page((unsigned long)bpage->page);
 	kfree(bpage);
 }
 
@@ -246,7 +359,7 @@ static inline int test_time_stamp(u64 delta)
 	return 0;
 }
 
-#define BUF_PAGE_SIZE (PAGE_SIZE - offsetof(struct buffer_data_page, data))
+#define BUF_PAGE_SIZE (PAGE_SIZE - BUF_PAGE_HDR_SIZE)
 
 /*
  * head_page == tail_page && head == tail then buffer is empty.
@@ -260,7 +373,7 @@ struct ring_buffer_per_cpu {
 	struct list_head		pages;
 	struct buffer_page		*head_page;	/* read from head */
 	struct buffer_page		*tail_page;	/* write to tail */
-	struct buffer_page		*commit_page;	/* commited pages */
+	struct buffer_page		*commit_page;	/* committed pages */
 	struct buffer_page		*reader_page;
 	unsigned long			overrun;
 	unsigned long			entries;
@@ -273,12 +386,17 @@ struct ring_buffer {
 	unsigned			pages;
 	unsigned			flags;
 	int				cpus;
-	cpumask_var_t			cpumask;
 	atomic_t			record_disabled;
+	cpumask_var_t			cpumask;
 
 	struct mutex			mutex;
 
 	struct ring_buffer_per_cpu	**buffers;
+
+#ifdef CONFIG_HOTPLUG_CPU
+	struct notifier_block		cpu_notify;
+#endif
+	u64				(*clock)(void);
 };
 
 struct ring_buffer_iter {
@@ -299,11 +417,35 @@ struct ring_buffer_iter {
 		_____ret;					\
 	})
 
+/* Up this if you want to test the TIME_EXTENTS and normalization */
+#define DEBUG_SHIFT 0
+
+u64 ring_buffer_time_stamp(struct ring_buffer *buffer, int cpu)
+{
+	u64 time;
+
+	preempt_disable_notrace();
+	/* shift to debug/test normalization and TIME_EXTENTS */
+	time = buffer->clock() << DEBUG_SHIFT;
+	preempt_enable_no_resched_notrace();
+
+	return time;
+}
+EXPORT_SYMBOL_GPL(ring_buffer_time_stamp);
+
+void ring_buffer_normalize_time_stamp(struct ring_buffer *buffer,
+				      int cpu, u64 *ts)
+{
+	/* Just stupid testing the normalize function and deltas */
+	*ts >>= DEBUG_SHIFT;
+}
+EXPORT_SYMBOL_GPL(ring_buffer_normalize_time_stamp);
+
 /**
  * check_pages - integrity check of buffer pages
  * @cpu_buffer: CPU buffer with pages to test
  *
- * As a safty measure we check to make sure the data pages have not
+ * As a safety measure we check to make sure the data pages have not
  * been corrupted.
  */
 static int rb_check_pages(struct ring_buffer_per_cpu *cpu_buffer)
@@ -421,7 +563,6 @@ static void rb_free_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer)
 	struct list_head *head = &cpu_buffer->pages;
 	struct buffer_page *bpage, *tmp;
 
-	list_del_init(&cpu_buffer->reader_page->list);
 	free_buffer_page(cpu_buffer->reader_page);
 
 	list_for_each_entry_safe(bpage, tmp, head, list) {
@@ -437,6 +578,11 @@ static void rb_free_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer)
  */
 extern int ring_buffer_page_too_big(void);
 
+#ifdef CONFIG_HOTPLUG_CPU
+static int rb_cpu_notify(struct notifier_block *self,
+			 unsigned long action, void *hcpu);
+#endif
+
 /**
  * ring_buffer_alloc - allocate a new ring_buffer
  * @size: the size in bytes per cpu that is needed.
@@ -469,12 +615,23 @@ struct ring_buffer *ring_buffer_alloc(unsigned long size, unsigned flags)
 
 	buffer->pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
 	buffer->flags = flags;
+	buffer->clock = trace_clock_local;
 
 	/* need at least two pages */
 	if (buffer->pages == 1)
 		buffer->pages++;
 
+	/*
+	 * In case of non-hotplug cpu, if the ring-buffer is allocated
+	 * in early initcall, it will not be notified of secondary cpus.
+	 * In that off case, we need to allocate for all possible cpus.
+	 */
+#ifdef CONFIG_HOTPLUG_CPU
+	get_online_cpus();
+	cpumask_copy(buffer->cpumask, cpu_online_mask);
+#else
 	cpumask_copy(buffer->cpumask, cpu_possible_mask);
+#endif
 	buffer->cpus = nr_cpu_ids;
 
 	bsize = sizeof(void *) * nr_cpu_ids;
@@ -490,6 +647,13 @@ struct ring_buffer *ring_buffer_alloc(unsigned long size, unsigned flags)
 			goto fail_free_buffers;
 	}
 
+#ifdef CONFIG_HOTPLUG_CPU
+	buffer->cpu_notify.notifier_call = rb_cpu_notify;
+	buffer->cpu_notify.priority = 0;
+	register_cpu_notifier(&buffer->cpu_notify);
+#endif
+
+	put_online_cpus();
 	mutex_init(&buffer->mutex);
 
 	return buffer;
@@ -503,6 +667,7 @@ struct ring_buffer *ring_buffer_alloc(unsigned long size, unsigned flags)
 
  fail_free_cpumask:
 	free_cpumask_var(buffer->cpumask);
+	put_online_cpus();
 
  fail_free_buffer:
 	kfree(buffer);
@@ -519,15 +684,29 @@ ring_buffer_free(struct ring_buffer *buffer)
 {
 	int cpu;
 
+	get_online_cpus();
+
+#ifdef CONFIG_HOTPLUG_CPU
+	unregister_cpu_notifier(&buffer->cpu_notify);
+#endif
+
 	for_each_buffer_cpu(buffer, cpu)
 		rb_free_cpu_buffer(buffer->buffers[cpu]);
 
+	put_online_cpus();
+
 	free_cpumask_var(buffer->cpumask);
 
 	kfree(buffer);
 }
 EXPORT_SYMBOL_GPL(ring_buffer_free);
 
+void ring_buffer_set_clock(struct ring_buffer *buffer,
+			   u64 (*clock)(void))
+{
+	buffer->clock = clock;
+}
+
 static void rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer);
 
 static void
@@ -627,16 +806,15 @@ int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size)
 		return size;
 
 	mutex_lock(&buffer->mutex);
+	get_online_cpus();
 
 	nr_pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
 
 	if (size < buffer_size) {
 
 		/* easy case, just free pages */
-		if (RB_WARN_ON(buffer, nr_pages >= buffer->pages)) {
-			mutex_unlock(&buffer->mutex);
-			return -1;
-		}
+		if (RB_WARN_ON(buffer, nr_pages >= buffer->pages))
+			goto out_fail;
 
 		rm_pages = buffer->pages - nr_pages;
 
@@ -655,10 +833,8 @@ int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size)
 	 * add these pages to the cpu_buffers. Otherwise we just free
 	 * them all and return -ENOMEM;
 	 */
-	if (RB_WARN_ON(buffer, nr_pages <= buffer->pages)) {
-		mutex_unlock(&buffer->mutex);
-		return -1;
-	}
+	if (RB_WARN_ON(buffer, nr_pages <= buffer->pages))
+		goto out_fail;
 
 	new_pages = nr_pages - buffer->pages;
 
@@ -683,13 +859,12 @@ int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size)
 		rb_insert_pages(cpu_buffer, &pages, new_pages);
 	}
 
-	if (RB_WARN_ON(buffer, !list_empty(&pages))) {
-		mutex_unlock(&buffer->mutex);
-		return -1;
-	}
+	if (RB_WARN_ON(buffer, !list_empty(&pages)))
+		goto out_fail;
 
  out:
 	buffer->pages = nr_pages;
+	put_online_cpus();
 	mutex_unlock(&buffer->mutex);
 
 	return size;
@@ -699,15 +874,20 @@ int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size)
 		list_del_init(&bpage->list);
 		free_buffer_page(bpage);
 	}
+	put_online_cpus();
 	mutex_unlock(&buffer->mutex);
 	return -ENOMEM;
-}
-EXPORT_SYMBOL_GPL(ring_buffer_resize);
 
-static inline int rb_null_event(struct ring_buffer_event *event)
-{
-	return event->type == RINGBUF_TYPE_PADDING;
+	/*
+	 * Something went totally wrong, and we are too paranoid
+	 * to even clean up the mess.
+	 */
+ out_fail:
+	put_online_cpus();
+	mutex_unlock(&buffer->mutex);
+	return -1;
 }
+EXPORT_SYMBOL_GPL(ring_buffer_resize);
 
 static inline void *
 __rb_data_page_index(struct buffer_data_page *bpage, unsigned index)
@@ -811,7 +991,7 @@ rb_event_index(struct ring_buffer_event *event)
 	return (addr & ~PAGE_MASK) - (PAGE_SIZE - BUF_PAGE_SIZE);
 }
 
-static inline int
+static int
 rb_is_commit(struct ring_buffer_per_cpu *cpu_buffer,
 	     struct ring_buffer_event *event)
 {
@@ -825,7 +1005,7 @@ rb_is_commit(struct ring_buffer_per_cpu *cpu_buffer,
 		rb_commit_index(cpu_buffer) == index;
 }
 
-static inline void
+static void
 rb_set_commit_event(struct ring_buffer_per_cpu *cpu_buffer,
 		    struct ring_buffer_event *event)
 {
@@ -850,7 +1030,7 @@ rb_set_commit_event(struct ring_buffer_per_cpu *cpu_buffer,
 	local_set(&cpu_buffer->commit_page->page->commit, index);
 }
 
-static inline void
+static void
 rb_set_commit_to_write(struct ring_buffer_per_cpu *cpu_buffer)
 {
 	/*
@@ -896,7 +1076,7 @@ static void rb_reset_reader_page(struct ring_buffer_per_cpu *cpu_buffer)
 	cpu_buffer->reader_page->read = 0;
 }
 
-static inline void rb_inc_iter(struct ring_buffer_iter *iter)
+static void rb_inc_iter(struct ring_buffer_iter *iter)
 {
 	struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
 
@@ -926,7 +1106,7 @@ static inline void rb_inc_iter(struct ring_buffer_iter *iter)
  * and with this, we can determine what to place into the
  * data field.
  */
-static inline void
+static void
 rb_update_event(struct ring_buffer_event *event,
 			 unsigned type, unsigned length)
 {
@@ -938,15 +1118,11 @@ rb_update_event(struct ring_buffer_event *event,
 		break;
 
 	case RINGBUF_TYPE_TIME_EXTEND:
-		event->len =
-			(RB_LEN_TIME_EXTEND + (RB_ALIGNMENT-1))
-			>> RB_ALIGNMENT_SHIFT;
+		event->len = DIV_ROUND_UP(RB_LEN_TIME_EXTEND, RB_ALIGNMENT);
 		break;
 
 	case RINGBUF_TYPE_TIME_STAMP:
-		event->len =
-			(RB_LEN_TIME_STAMP + (RB_ALIGNMENT-1))
-			>> RB_ALIGNMENT_SHIFT;
+		event->len = DIV_ROUND_UP(RB_LEN_TIME_STAMP, RB_ALIGNMENT);
 		break;
 
 	case RINGBUF_TYPE_DATA:
@@ -955,16 +1131,14 @@ rb_update_event(struct ring_buffer_event *event,
 			event->len = 0;
 			event->array[0] = length;
 		} else
-			event->len =
-				(length + (RB_ALIGNMENT-1))
-				>> RB_ALIGNMENT_SHIFT;
+			event->len = DIV_ROUND_UP(length, RB_ALIGNMENT);
 		break;
 	default:
 		BUG();
 	}
 }
 
-static inline unsigned rb_calculate_event_length(unsigned length)
+static unsigned rb_calculate_event_length(unsigned length)
 {
 	struct ring_buffer_event event; /* Used only for sizeof array */
 
@@ -990,6 +1164,7 @@ __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
 	struct ring_buffer *buffer = cpu_buffer->buffer;
 	struct ring_buffer_event *event;
 	unsigned long flags;
+	bool lock_taken = false;
 
 	commit_page = cpu_buffer->commit_page;
 	/* we just need to protect against interrupts */
@@ -1003,7 +1178,30 @@ __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
 		struct buffer_page *next_page = tail_page;
 
 		local_irq_save(flags);
-		__raw_spin_lock(&cpu_buffer->lock);
+		/*
+		 * Since the write to the buffer is still not
+		 * fully lockless, we must be careful with NMIs.
+		 * The locks in the writers are taken when a write
+		 * crosses to a new page. The locks protect against
+		 * races with the readers (this will soon be fixed
+		 * with a lockless solution).
+		 *
+		 * Because we can not protect against NMIs, and we
+		 * want to keep traces reentrant, we need to manage
+		 * what happens when we are in an NMI.
+		 *
+		 * NMIs can happen after we take the lock.
+		 * If we are in an NMI, only take the lock
+		 * if it is not already taken. Otherwise
+		 * simply fail.
+		 */
+		if (unlikely(in_nmi())) {
+			if (!__raw_spin_trylock(&cpu_buffer->lock))
+				goto out_reset;
+		} else
+			__raw_spin_lock(&cpu_buffer->lock);
+
+		lock_taken = true;
 
 		rb_inc_page(cpu_buffer, &next_page);
 
@@ -1012,7 +1210,7 @@ __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
 
 		/* we grabbed the lock before incrementing */
 		if (RB_WARN_ON(cpu_buffer, next_page == reader_page))
-			goto out_unlock;
+			goto out_reset;
 
 		/*
 		 * If for some reason, we had an interrupt storm that made
@@ -1021,12 +1219,12 @@ __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
 		 */
 		if (unlikely(next_page == commit_page)) {
 			WARN_ON_ONCE(1);
-			goto out_unlock;
+			goto out_reset;
 		}
 
 		if (next_page == head_page) {
 			if (!(buffer->flags & RB_FL_OVERWRITE))
-				goto out_unlock;
+				goto out_reset;
 
 			/* tail_page has not moved yet? */
 			if (tail_page == cpu_buffer->tail_page) {
@@ -1050,7 +1248,7 @@ __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
 			cpu_buffer->tail_page = next_page;
 
 			/* reread the time stamp */
-			*ts = ring_buffer_time_stamp(cpu_buffer->cpu);
+			*ts = ring_buffer_time_stamp(buffer, cpu_buffer->cpu);
 			cpu_buffer->tail_page->page->time_stamp = *ts;
 		}
 
@@ -1060,7 +1258,7 @@ __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
 		if (tail < BUF_PAGE_SIZE) {
 			/* Mark the rest of the page with padding */
 			event = __rb_page_index(tail_page, tail);
-			event->type = RINGBUF_TYPE_PADDING;
+			rb_event_set_padding(event);
 		}
 
 		if (tail <= BUF_PAGE_SIZE)
@@ -1100,12 +1298,13 @@ __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
 
 	return event;
 
- out_unlock:
+ out_reset:
 	/* reset write */
 	if (tail <= BUF_PAGE_SIZE)
 		local_set(&tail_page->write, tail);
 
-	__raw_spin_unlock(&cpu_buffer->lock);
+	if (likely(lock_taken))
+		__raw_spin_unlock(&cpu_buffer->lock);
 	local_irq_restore(flags);
 	return NULL;
 }
@@ -1192,7 +1391,7 @@ rb_reserve_next_event(struct ring_buffer_per_cpu *cpu_buffer,
 	if (RB_WARN_ON(cpu_buffer, ++nr_loops > 1000))
 		return NULL;
 
-	ts = ring_buffer_time_stamp(cpu_buffer->cpu);
+	ts = ring_buffer_time_stamp(cpu_buffer->buffer, cpu_buffer->cpu);
 
 	/*
 	 * Only the first commit can update the timestamp.
@@ -1265,7 +1464,6 @@ static DEFINE_PER_CPU(int, rb_need_resched);
  * ring_buffer_lock_reserve - reserve a part of the buffer
  * @buffer: the ring buffer to reserve from
  * @length: the length of the data to reserve (excluding event header)
- * @flags: a pointer to save the interrupt flags
  *
  * Returns a reseverd event on the ring buffer to copy directly to.
  * The user of this interface will need to get the body to write into
@@ -1278,9 +1476,7 @@ static DEFINE_PER_CPU(int, rb_need_resched);
  * If NULL is returned, then nothing has been allocated or locked.
  */
 struct ring_buffer_event *
-ring_buffer_lock_reserve(struct ring_buffer *buffer,
-			 unsigned long length,
-			 unsigned long *flags)
+ring_buffer_lock_reserve(struct ring_buffer *buffer, unsigned long length)
 {
 	struct ring_buffer_per_cpu *cpu_buffer;
 	struct ring_buffer_event *event;
@@ -1347,15 +1543,13 @@ static void rb_commit(struct ring_buffer_per_cpu *cpu_buffer,
  * ring_buffer_unlock_commit - commit a reserved
  * @buffer: The buffer to commit to
  * @event: The event pointer to commit.
- * @flags: the interrupt flags received from ring_buffer_lock_reserve.
  *
  * This commits the data to the ring buffer, and releases any locks held.
  *
  * Must be paired with ring_buffer_lock_reserve.
  */
 int ring_buffer_unlock_commit(struct ring_buffer *buffer,
-			      struct ring_buffer_event *event,
-			      unsigned long flags)
+			      struct ring_buffer_event *event)
 {
 	struct ring_buffer_per_cpu *cpu_buffer;
 	int cpu = raw_smp_processor_id();
@@ -1438,7 +1632,7 @@ int ring_buffer_write(struct ring_buffer *buffer,
 }
 EXPORT_SYMBOL_GPL(ring_buffer_write);
 
-static inline int rb_per_cpu_empty(struct ring_buffer_per_cpu *cpu_buffer)
+static int rb_per_cpu_empty(struct ring_buffer_per_cpu *cpu_buffer)
 {
 	struct buffer_page *reader = cpu_buffer->reader_page;
 	struct buffer_page *head = cpu_buffer->head_page;
@@ -1528,12 +1722,15 @@ EXPORT_SYMBOL_GPL(ring_buffer_record_enable_cpu);
 unsigned long ring_buffer_entries_cpu(struct ring_buffer *buffer, int cpu)
 {
 	struct ring_buffer_per_cpu *cpu_buffer;
+	unsigned long ret;
 
 	if (!cpumask_test_cpu(cpu, buffer->cpumask))
 		return 0;
 
 	cpu_buffer = buffer->buffers[cpu];
-	return cpu_buffer->entries;
+	ret = cpu_buffer->entries;
+
+	return ret;
 }
 EXPORT_SYMBOL_GPL(ring_buffer_entries_cpu);
 
@@ -1545,12 +1742,15 @@ EXPORT_SYMBOL_GPL(ring_buffer_entries_cpu);
 unsigned long ring_buffer_overrun_cpu(struct ring_buffer *buffer, int cpu)
 {
 	struct ring_buffer_per_cpu *cpu_buffer;
+	unsigned long ret;
 
 	if (!cpumask_test_cpu(cpu, buffer->cpumask))
 		return 0;
 
 	cpu_buffer = buffer->buffers[cpu];
-	return cpu_buffer->overrun;
+	ret = cpu_buffer->overrun;
+
+	return ret;
 }
 EXPORT_SYMBOL_GPL(ring_buffer_overrun_cpu);
 
@@ -1627,9 +1827,14 @@ static void rb_iter_reset(struct ring_buffer_iter *iter)
  */
 void ring_buffer_iter_reset(struct ring_buffer_iter *iter)
 {
-	struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
+	struct ring_buffer_per_cpu *cpu_buffer;
 	unsigned long flags;
 
+	if (!iter)
+		return;
+
+	cpu_buffer = iter->cpu_buffer;
+
 	spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
 	rb_iter_reset(iter);
 	spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
@@ -1803,7 +2008,7 @@ static void rb_advance_reader(struct ring_buffer_per_cpu *cpu_buffer)
 
 	event = rb_reader_event(cpu_buffer);
 
-	if (event->type == RINGBUF_TYPE_DATA)
+	if (event->type == RINGBUF_TYPE_DATA || rb_discarded_event(event))
 		cpu_buffer->entries--;
 
 	rb_update_read_stamp(cpu_buffer, event);
@@ -1864,9 +2069,6 @@ rb_buffer_peek(struct ring_buffer *buffer, int cpu, u64 *ts)
 	struct buffer_page *reader;
 	int nr_loops = 0;
 
-	if (!cpumask_test_cpu(cpu, buffer->cpumask))
-		return NULL;
-
 	cpu_buffer = buffer->buffers[cpu];
 
  again:
@@ -1889,9 +2091,18 @@ rb_buffer_peek(struct ring_buffer *buffer, int cpu, u64 *ts)
 
 	switch (event->type) {
 	case RINGBUF_TYPE_PADDING:
-		RB_WARN_ON(cpu_buffer, 1);
+		if (rb_null_event(event))
+			RB_WARN_ON(cpu_buffer, 1);
+		/*
+		 * Because the writer could be discarding every
+		 * event it creates (which would probably be bad)
+		 * if we were to go back to "again" then we may never
+		 * catch up, and will trigger the warn on, or lock
+		 * the box. Return the padding, and we will release
+		 * the current locks, and try again.
+		 */
 		rb_advance_reader(cpu_buffer);
-		return NULL;
+		return event;
 
 	case RINGBUF_TYPE_TIME_EXTEND:
 		/* Internal data, OK to advance */
@@ -1906,7 +2117,8 @@ rb_buffer_peek(struct ring_buffer *buffer, int cpu, u64 *ts)
 	case RINGBUF_TYPE_DATA:
 		if (ts) {
 			*ts = cpu_buffer->read_stamp + event->time_delta;
-			ring_buffer_normalize_time_stamp(cpu_buffer->cpu, ts);
+			ring_buffer_normalize_time_stamp(buffer,
+							 cpu_buffer->cpu, ts);
 		}
 		return event;
 
@@ -1951,8 +2163,12 @@ rb_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
 
 	switch (event->type) {
 	case RINGBUF_TYPE_PADDING:
-		rb_inc_iter(iter);
-		goto again;
+		if (rb_null_event(event)) {
+			rb_inc_iter(iter);
+			goto again;
+		}
+		rb_advance_iter(iter);
+		return event;
 
 	case RINGBUF_TYPE_TIME_EXTEND:
 		/* Internal data, OK to advance */
@@ -1967,7 +2183,8 @@ rb_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
 	case RINGBUF_TYPE_DATA:
 		if (ts) {
 			*ts = iter->read_stamp + event->time_delta;
-			ring_buffer_normalize_time_stamp(cpu_buffer->cpu, ts);
+			ring_buffer_normalize_time_stamp(buffer,
+							 cpu_buffer->cpu, ts);
 		}
 		return event;
 
@@ -1995,10 +2212,19 @@ ring_buffer_peek(struct ring_buffer *buffer, int cpu, u64 *ts)
 	struct ring_buffer_event *event;
 	unsigned long flags;
 
+	if (!cpumask_test_cpu(cpu, buffer->cpumask))
+		return NULL;
+
+ again:
 	spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
 	event = rb_buffer_peek(buffer, cpu, ts);
 	spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
 
+	if (event && event->type == RINGBUF_TYPE_PADDING) {
+		cpu_relax();
+		goto again;
+	}
+
 	return event;
 }
 
@@ -2017,10 +2243,16 @@ ring_buffer_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
 	struct ring_buffer_event *event;
 	unsigned long flags;
 
+ again:
 	spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
 	event = rb_iter_peek(iter, ts);
 	spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
 
+	if (event && event->type == RINGBUF_TYPE_PADDING) {
+		cpu_relax();
+		goto again;
+	}
+
 	return event;
 }
 
@@ -2035,24 +2267,37 @@ ring_buffer_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
 struct ring_buffer_event *
 ring_buffer_consume(struct ring_buffer *buffer, int cpu, u64 *ts)
 {
-	struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
-	struct ring_buffer_event *event;
+	struct ring_buffer_per_cpu *cpu_buffer;
+	struct ring_buffer_event *event = NULL;
 	unsigned long flags;
 
+ again:
+	/* might be called in atomic */
+	preempt_disable();
+
 	if (!cpumask_test_cpu(cpu, buffer->cpumask))
-		return NULL;
+		goto out;
 
+	cpu_buffer = buffer->buffers[cpu];
 	spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
 
 	event = rb_buffer_peek(buffer, cpu, ts);
 	if (!event)
-		goto out;
+		goto out_unlock;
 
 	rb_advance_reader(cpu_buffer);
 
- out:
+ out_unlock:
 	spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
 
+ out:
+	preempt_enable();
+
+	if (event && event->type == RINGBUF_TYPE_PADDING) {
+		cpu_relax();
+		goto again;
+	}
+
 	return event;
 }
 EXPORT_SYMBOL_GPL(ring_buffer_consume);
@@ -2131,6 +2376,7 @@ ring_buffer_read(struct ring_buffer_iter *iter, u64 *ts)
 	struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
 	unsigned long flags;
 
+ again:
 	spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
 	event = rb_iter_peek(iter, ts);
 	if (!event)
@@ -2140,6 +2386,11 @@ ring_buffer_read(struct ring_buffer_iter *iter, u64 *ts)
  out:
 	spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
 
+	if (event && event->type == RINGBUF_TYPE_PADDING) {
+		cpu_relax();
+		goto again;
+	}
+
 	return event;
 }
 EXPORT_SYMBOL_GPL(ring_buffer_read);
@@ -2232,6 +2483,7 @@ int ring_buffer_empty(struct ring_buffer *buffer)
 		if (!rb_per_cpu_empty(cpu_buffer))
 			return 0;
 	}
+
 	return 1;
 }
 EXPORT_SYMBOL_GPL(ring_buffer_empty);
@@ -2244,12 +2496,16 @@ EXPORT_SYMBOL_GPL(ring_buffer_empty);
 int ring_buffer_empty_cpu(struct ring_buffer *buffer, int cpu)
 {
 	struct ring_buffer_per_cpu *cpu_buffer;
+	int ret;
 
 	if (!cpumask_test_cpu(cpu, buffer->cpumask))
 		return 1;
 
 	cpu_buffer = buffer->buffers[cpu];
-	return rb_per_cpu_empty(cpu_buffer);
+	ret = rb_per_cpu_empty(cpu_buffer);
+
+
+	return ret;
 }
 EXPORT_SYMBOL_GPL(ring_buffer_empty_cpu);
 
@@ -2268,18 +2524,36 @@ int ring_buffer_swap_cpu(struct ring_buffer *buffer_a,
 {
 	struct ring_buffer_per_cpu *cpu_buffer_a;
 	struct ring_buffer_per_cpu *cpu_buffer_b;
+	int ret = -EINVAL;
 
 	if (!cpumask_test_cpu(cpu, buffer_a->cpumask) ||
 	    !cpumask_test_cpu(cpu, buffer_b->cpumask))
-		return -EINVAL;
+		goto out;
 
 	/* At least make sure the two buffers are somewhat the same */
 	if (buffer_a->pages != buffer_b->pages)
-		return -EINVAL;
+		goto out;
+
+	ret = -EAGAIN;
+
+	if (ring_buffer_flags != RB_BUFFERS_ON)
+		goto out;
+
+	if (atomic_read(&buffer_a->record_disabled))
+		goto out;
+
+	if (atomic_read(&buffer_b->record_disabled))
+		goto out;
 
 	cpu_buffer_a = buffer_a->buffers[cpu];
 	cpu_buffer_b = buffer_b->buffers[cpu];
 
+	if (atomic_read(&cpu_buffer_a->record_disabled))
+		goto out;
+
+	if (atomic_read(&cpu_buffer_b->record_disabled))
+		goto out;
+
 	/*
 	 * We can't do a synchronize_sched here because this
 	 * function can be called in atomic context.
@@ -2298,18 +2572,21 @@ int ring_buffer_swap_cpu(struct ring_buffer *buffer_a,
 	atomic_dec(&cpu_buffer_a->record_disabled);
 	atomic_dec(&cpu_buffer_b->record_disabled);
 
-	return 0;
+	ret = 0;
+out:
+	return ret;
 }
 EXPORT_SYMBOL_GPL(ring_buffer_swap_cpu);
 
 static void rb_remove_entries(struct ring_buffer_per_cpu *cpu_buffer,
-			      struct buffer_data_page *bpage)
+			      struct buffer_data_page *bpage,
+			      unsigned int offset)
 {
 	struct ring_buffer_event *event;
 	unsigned long head;
 
 	__raw_spin_lock(&cpu_buffer->lock);
-	for (head = 0; head < local_read(&bpage->commit);
+	for (head = offset; head < local_read(&bpage->commit);
 	     head += rb_event_length(event)) {
 
 		event = __rb_data_page_index(bpage, head);
@@ -2340,8 +2617,8 @@ static void rb_remove_entries(struct ring_buffer_per_cpu *cpu_buffer,
  */
 void *ring_buffer_alloc_read_page(struct ring_buffer *buffer)
 {
-	unsigned long addr;
 	struct buffer_data_page *bpage;
+	unsigned long addr;
 
 	addr = __get_free_page(GFP_KERNEL);
 	if (!addr)
@@ -2349,6 +2626,8 @@ void *ring_buffer_alloc_read_page(struct ring_buffer *buffer)
 
 	bpage = (void *)addr;
 
+	rb_init_page(bpage);
+
 	return bpage;
 }
 
@@ -2368,6 +2647,7 @@ void ring_buffer_free_read_page(struct ring_buffer *buffer, void *data)
  * ring_buffer_read_page - extract a page from the ring buffer
  * @buffer: buffer to extract from
  * @data_page: the page to use allocated from ring_buffer_alloc_read_page
+ * @len: amount to extract
  * @cpu: the cpu of the buffer to extract
  * @full: should the extraction only happen when the page is full.
  *
@@ -2377,12 +2657,12 @@ void ring_buffer_free_read_page(struct ring_buffer *buffer, void *data)
  * to swap with a page in the ring buffer.
  *
  * for example:
- *	rpage = ring_buffer_alloc_page(buffer);
+ *	rpage = ring_buffer_alloc_read_page(buffer);
  *	if (!rpage)
  *		return error;
- *	ret = ring_buffer_read_page(buffer, &rpage, cpu, 0);
- *	if (ret)
- *		process_page(rpage);
+ *	ret = ring_buffer_read_page(buffer, &rpage, len, cpu, 0);
+ *	if (ret >= 0)
+ *		process_page(rpage, ret);
  *
  * When @full is set, the function will not return true unless
  * the writer is off the reader page.
@@ -2393,72 +2673,118 @@ void ring_buffer_free_read_page(struct ring_buffer *buffer, void *data)
  *  responsible for that.
  *
  * Returns:
- *  1 if data has been transferred
- *  0 if no data has been transferred.
+ *  >=0 if data has been transferred, returns the offset of consumed data.
+ *  <0 if no data has been transferred.
  */
 int ring_buffer_read_page(struct ring_buffer *buffer,
-			    void **data_page, int cpu, int full)
+			  void **data_page, size_t len, int cpu, int full)
 {
 	struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
 	struct ring_buffer_event *event;
 	struct buffer_data_page *bpage;
+	struct buffer_page *reader;
 	unsigned long flags;
-	int ret = 0;
+	unsigned int commit;
+	unsigned int read;
+	u64 save_timestamp;
+	int ret = -1;
+
+	if (!cpumask_test_cpu(cpu, buffer->cpumask))
+		goto out;
+
+	/*
+	 * If len is not big enough to hold the page header, then
+	 * we can not copy anything.
+	 */
+	if (len <= BUF_PAGE_HDR_SIZE)
+		goto out;
+
+	len -= BUF_PAGE_HDR_SIZE;
 
 	if (!data_page)
-		return 0;
+		goto out;
 
 	bpage = *data_page;
 	if (!bpage)
-		return 0;
+		goto out;
 
 	spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
 
-	/*
-	 * rb_buffer_peek will get the next ring buffer if
-	 * the current reader page is empty.
-	 */
-	event = rb_buffer_peek(buffer, cpu, NULL);
-	if (!event)
-		goto out;
+	reader = rb_get_reader_page(cpu_buffer);
+	if (!reader)
+		goto out_unlock;
+
+	event = rb_reader_event(cpu_buffer);
+
+	read = reader->read;
+	commit = rb_page_commit(reader);
 
-	/* check for data */
-	if (!local_read(&cpu_buffer->reader_page->page->commit))
-		goto out;
 	/*
-	 * If the writer is already off of the read page, then simply
-	 * switch the read page with the given page. Otherwise
-	 * we need to copy the data from the reader to the writer.
+	 * If this page has been partially read or
+	 * if len is not big enough to read the rest of the page or
+	 * a writer is still on the page, then
+	 * we must copy the data from the page to the buffer.
+	 * Otherwise, we can simply swap the page with the one passed in.
 	 */
-	if (cpu_buffer->reader_page == cpu_buffer->commit_page) {
-		unsigned int read = cpu_buffer->reader_page->read;
+	if (read || (len < (commit - read)) ||
+	    cpu_buffer->reader_page == cpu_buffer->commit_page) {
+		struct buffer_data_page *rpage = cpu_buffer->reader_page->page;
+		unsigned int rpos = read;
+		unsigned int pos = 0;
+		unsigned int size;
 
 		if (full)
-			goto out;
-		/* The writer is still on the reader page, we must copy */
-		bpage = cpu_buffer->reader_page->page;
-		memcpy(bpage->data,
-		       cpu_buffer->reader_page->page->data + read,
-		       local_read(&bpage->commit) - read);
+			goto out_unlock;
+
+		if (len > (commit - read))
+			len = (commit - read);
+
+		size = rb_event_length(event);
+
+		if (len < size)
+			goto out_unlock;
 
-		/* consume what was read */
-		cpu_buffer->reader_page += read;
+		/* save the current timestamp, since the user will need it */
+		save_timestamp = cpu_buffer->read_stamp;
 
+		/* Need to copy one event at a time */
+		do {
+			memcpy(bpage->data + pos, rpage->data + rpos, size);
+
+			len -= size;
+
+			rb_advance_reader(cpu_buffer);
+			rpos = reader->read;
+			pos += size;
+
+			event = rb_reader_event(cpu_buffer);
+			size = rb_event_length(event);
+		} while (len > size);
+
+		/* update bpage */
+		local_set(&bpage->commit, pos);
+		bpage->time_stamp = save_timestamp;
+
+		/* we copied everything to the beginning */
+		read = 0;
 	} else {
 		/* swap the pages */
 		rb_init_page(bpage);
-		bpage = cpu_buffer->reader_page->page;
-		cpu_buffer->reader_page->page = *data_page;
-		cpu_buffer->reader_page->read = 0;
+		bpage = reader->page;
+		reader->page = *data_page;
+		local_set(&reader->write, 0);
+		reader->read = 0;
 		*data_page = bpage;
+
+		/* update the entry counter */
+		rb_remove_entries(cpu_buffer, bpage, read);
 	}
-	ret = 1;
+	ret = read;
 
-	/* update the entry counter */
-	rb_remove_entries(cpu_buffer, bpage);
- out:
+ out_unlock:
 	spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
 
+ out:
 	return ret;
 }
 
@@ -2466,7 +2792,7 @@ static ssize_t
 rb_simple_read(struct file *filp, char __user *ubuf,
 	       size_t cnt, loff_t *ppos)
 {
-	long *p = filp->private_data;
+	unsigned long *p = filp->private_data;
 	char buf[64];
 	int r;
 
@@ -2482,9 +2808,9 @@ static ssize_t
 rb_simple_write(struct file *filp, const char __user *ubuf,
 		size_t cnt, loff_t *ppos)
 {
-	long *p = filp->private_data;
+	unsigned long *p = filp->private_data;
 	char buf[64];
-	long val;
+	unsigned long val;
 	int ret;
 
 	if (cnt >= sizeof(buf))
@@ -2509,7 +2835,7 @@ rb_simple_write(struct file *filp, const char __user *ubuf,
 	return cnt;
 }
 
-static struct file_operations rb_simple_fops = {
+static const struct file_operations rb_simple_fops = {
 	.open		= tracing_open_generic,
 	.read		= rb_simple_read,
 	.write		= rb_simple_write,
@@ -2532,3 +2858,42 @@ static __init int rb_init_debugfs(void)
 }
 
 fs_initcall(rb_init_debugfs);
+
+#ifdef CONFIG_HOTPLUG_CPU
+static int rb_cpu_notify(struct notifier_block *self,
+			 unsigned long action, void *hcpu)
+{
+	struct ring_buffer *buffer =
+		container_of(self, struct ring_buffer, cpu_notify);
+	long cpu = (long)hcpu;
+
+	switch (action) {
+	case CPU_UP_PREPARE:
+	case CPU_UP_PREPARE_FROZEN:
+		if (cpu_isset(cpu, *buffer->cpumask))
+			return NOTIFY_OK;
+
+		buffer->buffers[cpu] =
+			rb_allocate_cpu_buffer(buffer, cpu);
+		if (!buffer->buffers[cpu]) {
+			WARN(1, "failed to allocate ring buffer on CPU %ld\n",
+			     cpu);
+			return NOTIFY_OK;
+		}
+		smp_wmb();
+		cpu_set(cpu, *buffer->cpumask);
+		break;
+	case CPU_DOWN_PREPARE:
+	case CPU_DOWN_PREPARE_FROZEN:
+		/*
+		 * Do nothing.
+		 *  If we were to free the buffer, then the user would
+		 *  lose any trace that was in the buffer.
+		 */
+		break;
+	default:
+		break;
+	}
+	return NOTIFY_OK;
+}
+#endif